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/*
* Copyright 2019 The Android Open Source Project
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package androidx.paging
import kotlinx.coroutines.ExperimentalCoroutinesApi
import kotlinx.coroutines.FlowPreview
import kotlinx.coroutines.channels.ConflatedBroadcastChannel
import kotlinx.coroutines.flow.asFlow
import kotlinx.coroutines.flow.filterNotNull
import kotlinx.coroutines.flow.mapLatest
import kotlinx.coroutines.flow.onStart
import kotlinx.coroutines.flow.scan
@UseExperimental(ExperimentalCoroutinesApi::class)
internal class PageFetcher<Key : Any, Value : Any>(
private val pagingSourceFactory: () -> PagingSource<Key, Value>,
private val initialKey: Key?,
private val config: PagingConfig
) {
// NOTE: This channel is conflated, which means it has a buffer size of 1, and will always
// broadcast the latest value received.
private var refreshChannel = ConflatedBroadcastChannel<Unit>()
// The object built by paging builder can maintain the scope so that on rotation we don't stop
// the paging.
@UseExperimental(FlowPreview::class)
val flow = refreshChannel
.asFlow()
.onStart { emit(Unit) }
.scan(null) { previousGeneration: Pager<Key, Value>?, _ ->
val pagingSource = pagingSourceFactory()
val initialKey = when (previousGeneration) {
null -> initialKey
else -> when (val info = previousGeneration.refreshKeyInfo()) {
null -> previousGeneration.initialKey
else -> pagingSource.getRefreshKeyFromPage(info.indexInPage, info.page)
}
}
// Hook up refresh signals from DataSource / PagingSource.
pagingSource.registerInvalidatedCallback(::refresh)
previousGeneration?.pagingSource?.unregisterInvalidatedCallback(::refresh)
previousGeneration?.pagingSource?.invalidate() // Note: Invalidate is idempotent.
Pager(initialKey, pagingSource, config)
}
.filterNotNull()
.mapLatest { generation ->
PagingData(generation.pageEventFlow, PagerUiReceiver(generation))
}
fun refresh() {
refreshChannel.offer(Unit)
}
}
@UseExperimental(ExperimentalCoroutinesApi::class, FlowPreview::class)
internal class PagerUiReceiver<Key : Any, Value : Any> constructor(
private val pager: Pager<Key, Value>
) : UiReceiver {
override fun addHint(hint: ViewportHint) = pager.addHint(hint)
override fun retry() = pager.retry()
}
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